Method of stabilizing laser wavelength and laser device with stabilized wavelength

ABSTRACT

A method and apparatus for stabilizing the wavelength in a laser. The apparatus includes a first and second etalon for fine and rough tuning, respectively, of a laser oscillator. The output power and wavelength of the laser beam, for example, can be used to adjust these etalons to provide a constant output power and to counteract the change in etalon characteristics due to heat.

FIELD OF THE INVENTION

This invention relates to a method of stabilizing laser wavelength and alaser device with stabilized wavelength.

BACKGROUND OF THE INVENTION

FIG. 1 is a structural view showing a conventional narrow bandwidthlaser shown, for example, in a magazine called "CAN. J. PHYS. VOL 63('85) 214".

This FIG. shows a laser medium 1, a full reflection mirror 2, anincomplete reflection mirror 3, an etalon 4 for rough tuning, an etalon5 for fine tuning and a laser beam 6.

A brief description of the operation of this laser follows. In FIG. 1laser medium 1 is surrounded by a light resonator consisting of the fullreflection mirror 2 and the incomplete reflection mirror 3, wherebylight is amplified while being reflected within the light resonatornumerous times before exiting as laser beam 6. Some laser resonatorsfound in, for example, excimer lasers, semiconductor lasers, pigmentlasers and some types of solid-state lasers, have large oscillatingwavelengths. By inserting spectroscopy elements into the lightresonator, their oscillating wavelength width can be narrowed. Forexample, a laser beam extremely close to monocolor can be obtained byusing a plurality of Fabry-Perot etalons (hereinafter to be abbreviatedas etalon).

In the example of FIG. 1, two etalons, that is, the etalon 4 for roughtuning and the etalon 5 for fine tuning are inserted into the lightresonator. FIG. 2 shows various wavelength profiles describing theprinciple behind the narrowing of the oscillation width of the laser.FIG. 2(a) shows a spectroscopy characteristic of the etalon for roughtuning. The peak position λm₁ of the spectroscopy characteristic isrepresented by the following equation (1), ##EQU1##

Here, n is the index of refraction of a material existing between twomirrors forming the etalon, d is a distance between the mirrors, θ₁ isan angle when light is incident upon the etalon, and m is an integer.Peaks correspond to the different of value of m. As is clear fromequation (1), peak wavelength of the mountain can be changed arbitrarilyby changing the value of any of n, d, and θ. The distance between peaksis called free spectral range (hereinafter to be abbreviated as FSR),and is represented by the following equation (2). ##EQU2## The half bandwidth Δλ, of each peak is represented by the following equation (3).##EQU3## Here F₁ is called finesse and is determined by the performancecharacteristics of the etalon.

FIG. 2(c) shows the spectroscopy characteristic of the gain of a lasermedium. When spectroscopy elements do not exist in the light resonatorto narrow the wavelength of the light, light is amplified to become alaser beam over the entire wavelength in the range of the gain. FIG.2(a) illustrates the state where loss is minimized at only the positionof λ₀ due to the existence of the etalon for rough tuning. Thereforelight is amplified and oscillated at only the vicinity of thiswavelength, by deciding d₁ and the like so that the peak position λm₁ ofthe talon for rough tuning is equal to any wavelength λ₀ in the rangewhere gain exists, and the peaks other than λm₁ do not come into thewavelength where gain exists.

The minimum value of FSR₁ is determined when there is only one peak andfinesse F is determined by the performance characteristics of theetalon. Since the finesse value is about 20, there is a limit towavelength width which can be narrowed only by one etalon for roughtuning.

According to the present invention, another etalon for fine tuning 5 isused. A spectroscopy characteristic of the fine tuning etalon, forexample, is illustrated in FIG. 2(b). Therein, the peak wavelength λm₂should be λ₀ and FSR₂ should be FSR₂ ≧Δλ₁. When the wavelength to beamplified and oscillated is desired to be narrower, another etalon canbe used.

According to the invention, the laser beam, whose spectroscopycharacteristic was, for example, that illustrated in FIG. 2(c), is tooscillate only in a narrow range including λ₀ where each peak of theetalons overlap each other as a center as shown in FIG. 2(d). Actually,laser beams pass through the etalons numerous times during oscillation,whereby the wavelength width of the laser beam becomes 1/2-1/10 of thewavelength determined by two etalons.

In the way above mentioned, the wavelength of the laser beam can benarrowed as described in the aforesaid magazine, and stability in ashort duration can be achieved by improving the light resonator andmaking the incident angle θ small. However, stability in a long durationwill not occur due to thermal problems, such as wavelength shift due togeneration of heat several when the laser beam passes through theetalons. This problem is explained with reference to FIG. 3.

FIG. 3(a) illustrates an enlarged spectroscopy characteristic of theetalon for rough tuning, wherein the solid line shows the spectroscopycharacteristic immediately after oscillation. Generation of heat afteroscillation cause the etalons to deform. This deformation does notdegrade the characteristics of etalons, but it changes the gap length ofetalons and as a result shifts the wavelength. Equation (4) shows thebetween the shift quantity and the change of d due to the deformation ofthe etalons. ##EQU4## The direction of the wavelength shift isdetermined by the structure of the etalon and the like, and wavelengthshifts in a certain direction due to the generation of heat by the laserbeam occur when a specified etalon is used. The state of shift at thattime is shown by the broken line function in FIG. 3(a). The etalon forfine tuning also has a similar wavelength shift as shown in FIG. 3(b).The shift quantity of the etalon for fine tuning becomes smaller by thequantity which is the difference between the etalon distance d₂ and theetalon d₁ when d₂ is bigger than d₁.

The problem at that time is that the peak wavelengths λm₁ and λm₂ ofspectroscopy characteristic of the two etalons deviate. Lighttransmission quantity when the two wavelengths overlap is reducedcompared with the case where λm₁ =λm₂. The state of laser oscillation atthat time is shown in FIG. 3(c). After a long oscillation, the laseroutput wavelength-shifts from λm₁ =λm₂ and the output is reduced. Whenthe shift quantity is large, another mode oscillation other than theetalon for fine tuning can occur.

Conventional narrow band width laser devices do not have means forcompensating the wavelength shift due to thermal problems of the etalonsnor do they have means for stopping output reduction which occurs whentwo etalons are used. Therefore, it has a problem that it can only beapplied to a low output laser whose effect of thermal deformation issmall.

SUMMARY OF THE INVENTION

The method of stabilizing laser wavelength related to the presentinvention aims to stabilize the wavelength of laser beam by obtainingspectroscopy data from a part of a laser beam wavelength-selected fromtwo etalons and by controlling one etalon on the basis of the analyzedresult of laser beam spectrum. Further, an apparatus and methodaccording to the invention aim to restrict the reduction of a laser beamoutput by measuring change of laser output from a part of laser beam andby controlling another etalon according to the analysis of the aforesaidoutput change.

A laser device with stabilized wavelength according to anotherembodiment comprises a servo system which selects wavelengths by beingprovided with two etalons, that is, the etalon for fine tuning andetalon for rough tuning, transmits a part of the laser beam taken out ofthe laser oscillator to a wavelength monitor system to measureoscillation wavelength, and drives the etalon for fine tuning byaforesaid measured wavelength to vary wavelength, a power monitor systemconsisting of a power meter for measuring the variation of laser outputindependently of the wavelength monitor system, a device for recordingthe output variation, and a servo system for controlling the etalon forrough tuning on the basis of signals from said power monitor system.

According to another embodiment of the invention, a laser device withstabilized wavelength comprises a servo system which selects wavelengthsby providing two etalons, that is, an etalon for fine tuning and anetalon for rough tuning, transmits a part of a laser beam taken out ofthe laser oscillator to measure oscillation wavelength, changeswavelength by driving the fine turning etalon according to the firstservo system, measures the applied voltage to the laser medium, andcontrols the etalon for rough tuning on the basis of the variation ofmeasured applied voltage.

A laser device with stabilized wavelength according to a furtherembodiment of the present invention servo system which selectedwavelength by being provided with two etalons, that is, an etalon forfine tuning and an etalon for rough tuning, transmits a part of a laserbeam taken out of the laser oscillator to the wavelength monitor systemto measure the oscillation wavelength, drives the etalon for finetuning, and with a servo system which measures laser output at the powermonitor system, controls an applied voltage to the laser medium,measures applied voltage and controls the etalon for rough tuning on thebasis of the analyzed result.

A laser device with stabilized wavelength according to a still furtherembodiment of the present invention comprises a servo system whichselects wavelength by being provided with two etalons, that is, anetalon for fine tuning and an etalon for rough tuning, transmits a partof the laser beam taken out of the laser oscillator into the wavelengthmonitor system to measure oscillation wavelength, drives the etalon forfine tuning by the measured wavelength, varies wavelength, measures thelaser output at the power monitor system, executes control of appliedvoltage into the laser medium and controls the etalon for rough tuningwith time sharing to make laser output constant.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a structural view of the conventional narrow band width laser;

FIGS. 2(a)-2(d) illustrate various spectroscopy characteristics of alaser and etalons according to the invention;

FIGS. 3(a)-3(c) illustrate variations due to the difference inwavelength shifts to two etalons;

FIG. 4 is a structural view showing a wavelength stabilized laseraccording to one embodiment of the present invention using thewavelength monitor system and the power monitor system;

FIG. 5 is a structural view showing a wavelength monitor system;

FIG. 6 is a distributional graph showing the intensity distribution ofinterference fringe on the pick up element of the wavelength monitorsystem;

FIG. 7 is a flow chart showing the outline of a method of stabilizinglaser wavelength according to the invention;

FIG. 8 is another flow chart showing the outline of a method ofstabilizing laser wavelength in the case where the laser device withstabilized wavelength shown in FIG. 4 is used;

FIG. 9 is a structural view showing laser with stabilized wavelengthaccording to another embodiment of the present invention using anapplied voltage generating system;

FIG. 10 is another flow chart showing the outline of a method ofstabilizing laser wavelength in the case where the laser device withstabilized wavelength shown in FIG. 5 is used;

FIG. 11 is a flow chart showing parallel control of the laser output;

FIG. 12 is a flow chart illustrating laser output with time sharing;

FIG. 13 is a laser device with stabilized wavelength for performing themethod illustrated in FIG. 11; and

FIG. 14 is a laser device with stabilized wavelength for performing themethod illustrated in FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the invention is discussed with reference toFIGS. 4 and 5. In FIG. 4 and FIG. 5, references numerals 1-5 identifyelements similar to those described with respect to FIG. 1, above. Thelaser device according to this embodiment further comprises a laser beam6, a wavelength monitor system 7, a control system 8, a power monitorsystem 9, servo systems 10 and 11 for controlling the etalons, anintegrator 12, a Fabry-Perot etalon 13, a focusing lens 14, a pick upelement 15 for observing an interference fringe caused by Fabry-perotetalon 13 and is, for example, a one dimensional image sensor, and animage processing unit 16 for analyzing the interference fringe.

Next, the operation of this laser device is described. In the same wayas the conventional laser device, this embodiment of the invention cangenerate a laser beam 6 of arbitrary wavelength λ₀ which is narrow inoscillation wavelength and in the range where gain exists. However, thelaser beam with these characteristics is unstabilized in wavelength andoutput as described previously, thus the control system for the etalonsto be described in the following is required.

First of all, the control system of the etalon for fine tuning isdescribed.

In FIG. 5, a part of the laser beam 6 is led to the wavelength monitorsystem. The wavelength monitor system 7 uses, for example, as shown in"IEEE Journal Quantum Electronics QE-14 ('78)17" etalon, prism, grating,Fizeau's interferometer and the like which obtain spectroscopy data. Inthe embodiment of the invention shown in FIG. 5, this wavelength monitorsystem is described wherein an etalon and a pick up element are used.

The wavelength monitor system consists of an integrator 12 for weakeningand dispersing the laser beam, etalon 13 and a lens 14. Among thediverged components created by the integrator 12, only components havinga specified incident angle can pass through the etalon and each focusinglens 14. Assuming that the focus distance of the lens is f, the lighthaving a component of θ gathers at a position away from the axis of thelens by fθ on the focus point to form a circular interference fringe.Hereupon, by observing, using the pick up element, the position wherelights gather, θ can be obtained, thereby λ can be calculated accordingto the equation of transmission wavelength of etalon previously shown.

Light intensity distribution on the pick up element is illustrated inFIG. 6. The y-axis shows output, and the x-axis shows a distance f fromthe center of the interference fringe. Each peak corresponds to thedifferent values m of a degree of the etalon. The distance between eachpeak is called free spectral range, and the wavelength can be determinedin the range. In addition, as the free spectral range is determined bythe design of FP, the wavelength shift should be designed wider than isexpected.

Since the peak has a light intensity distribution corresponding to thewavelength distribution of the laser beam, an image processing unit 16is required. Image processing unit 16 calculates the present wavelengthλ and wavelength adjustment of the oscillator is executed through theservo system 10.

FIG. 7(A) is a flow chart illustrating a method of stabilizing laserwavelength and shows an example of executing control of oscillationwavelength.

In Step 17, spectroscopy data is obtained from the laser beam by etalon13, and in Step 18, one dimensional light intensity distribution ismeasured by the pick up element. In Step 19, the measured data isblurred, and an image processing is executed such as removing noise andthe like. In Step 20, the position x which shows the maximum intensityis compared with the value x₀ (designated position coordinatecorresponding to designated wavelength), and when they are differentfrom each other, the etalon for fine tuning 5 is controlled throughservo system 10 according to x>x₀ or x<x₀. The central wavelength λm₂ ofthe transmission range of the etalon is then changed (Step 22), andprocessing returns to Step 17 and repeats this operation until x=x₀. Inthis manner, oscillation wavelength is kept constant by adjusting theetalon for fine tuning.

Next, the control system of an etalon for rough tuning is described. InFIG. 4, a part of the laser beam is introduced into the power monitor 9.The power monitor 9 consists of a part for measuring the laser outputand a part for recording the obtained laser output. When the etalon forrough tuning is controlled in either direction, it determines how toadjust the etalon for rough tuning 4 next. According to thedetermination, the central wavelength λm₂ of the etalon for rough tuning4 is adjusted by the servo system 11. The flow chart of this adjustmentis shown in FIG. 8(B). When the laser oscillation begins, shiftingoccurs as shown in FIG. 3, thereby changing the laser output. Thereupon,in Step 23, the output p is measured, the result thereof being recorded,and in Step 25, the result is compared with the previous measured resultp₀. When the outputs are different from each other, the etalon for roughtuning is adjusted by using servo system 11 according to p>p₀ or p<p₀.The process is continued until the etalon for rough tuning 4 reachesheat balance and the laser output is constant.

The control of two etalons 4 and 5 can be executed simultaneously, but,for example, laser output can be varied on account of moving the centralwavelength of the etalon for fine tuning 5 too much, therefor disorderedcontrol can accelerate the output change. To monitor both of thecontrols, the control system 8 selects the (A) or (B) control of theearliest part of the flow chart shown in FIG. 7. In this embodiment, (B)is given priority immediately after the laser oscillation, and (A) isgiven priority after the operation is stabilized to a certain degree.

The control of the etalon for rough tuning 4 in the case where an objectvalue (object value<laser maximum output) is set to the laser output,the laser output is stabilized to the object value and a noncontrolperiod is provided immediately after the oscillation start, is explainedreferring to the flow chart illustrated in FIG. 8. First of all, in Step26, the laser output is measured, and in Step 27, present laser outputP_(N) is calculated by the average value processing of N-number times ofmeasured data, and in Step 28, the absolute value |Px| of the differencebetween the present laser output P_(N) and the laser output object value(value which can be set from exterior) is calculated. Next, it isdetermined whether or not the time from the beginning of the oscillationis within the non-control duration, and if it is within the non-controlperiod, the etalon for rough tuning 4 is not controlled, and theprocessing returns to Step 26 after confirming that the laser isoscillating. When the time from the beginning of the oscillation exceedsthe noncontrol period, aforesaid |Px| is compared with a variationpermissive value (the value which can be set from the exterior) of thedesignated laser output P_(A). When |Px|<P_(A), the control of theetalon for rough tuning is not executed, and the processing returns toStep 26, when |Px|>P_(A), in Step 29, the control quantity is calculatedby |Px|. In Step 30, the control direction is determined from thepolarity of Px=P_(N) -P₀, and in Step 31, the servo system 11 is drivenand the etalon for rough tuning 4 is adjusted so that the laser outputcoincides with the set object value. By continuing the adjustment duringthe control laser oscillation, stabilization of the laser output ispossible for extended periods of time.

The control system above described executes the control of the etalonfor rough tuning by monitoring the laser output by means of the powermonitor. However, according to another preferred embodiment illustratedin FIGS. 9 and 10, the control can be executed using an applied voltagegenerating system instead of the power monitor. Further, the laseroutput control can be executed, as shown in FIG. 11, in parallel to boththe control of the applied voltage control and the control of the roughetalon, or can be controlled, as shown in FIG. 12, with time sharing.First of all, explanation is given on the parallel control shown in FIG.11. The device in this case is, for example, shown in FIG. 13.

First, the control of the applied voltage is described. The laser outputis measured at the power monitor system 8, and this measured data isaverage-mean-processed N times by an applied voltage generating means32, thereby calculating the present laser output value P_(N). Next, theabsolute value |ΔP|=P_(N) -P₀ of the difference between P_(N) and thedesignated laser output value P₀ (the value which can be set from theexterior) is calculated, then the value |ΔP| is compared with thevariation permissive value P_(A) (the value which can be set from theexterior) of the designated laser output, and in the case where|ΔP|≦P_(A), oscillation continues with the present applied voltageintact. On the other hand, in the case where |ΔP|>P, the controlquantity of the applied voltage is calculated from |ΔP|. Next, thecontrol direction of the applied voltage is determined from the polarityof ΔP=P_(N) -P₀, and the applied voltage is controlled so that the laseroutput becomes constant according to the aforesaid control quantity andcontrol direction.

Next, the control of the etalon for rough tuning is described. First, inStep 33, the applied voltage from the applied voltage generating means32 to the laser medium is measured by the control system 8. Next, inStep 34, the measured data is measured M times, average-mean-processedand the present applied voltage value V_(N) is calculated, and in Step35, the difference ΔV=V_(N) -V_(O) between V_(N) and the designatedobject applied voltage value V_(O) (the value which can be set from theexterior) is calculated and recorded. But, since the oscillation isunstable immediately after the oscillation, as in Step 36, for thecontrol of the etalon for rough tuning 4, the noncontrol period isprovided, and during this period the processing to calculate aforesaidΔV is executed without control of the etalon for rough tuning 4. Whenthe laser oscillation time exceeds the noncontrol period, in Step 37,|ΔV| is compared with the variation permissive value V_(A) (the valuewhich can be set from the exterior), and in the case where ΔV≦V_(A), thecontrol of the etalon for rough tuning 4 is not carried out and theoscillation is continued.

On the other hand, in the case where ΔV≦V_(A), in Step 38, the controlquantity of the etalon for rough tuning 4 is calculated from the valueof ΔV, and in Step 41, the servo system 11 is driven and the etalon forrough tuning 4 is adjusted so that ΔV is minimized. In the beginning,the control quantity of etalon is changed to the designated controldirection, and in Step 39, the present ΔV is compared with the previousΔV. In the case where the preceeding ΔV< the present ΔV, in Step 40, thecontrol quantity of the etalon is changed to the opposite direction. InStep 41, the servo system is driven and the etalon tuning is adjusted.

As described above, the laser output can be controlled to be constant bycontinuing control of the applied voltage and the etalon for roughtuning 4 by the laser during oscillation.

The control of the two etalons 4 and 5 can be executed simultaneously,but there is a possibility, for example, that the laser output will varybecause of extreme movement of the central wavelength of the etalon forfine tuning 5 and there is also a possibility that the output variationwill accelerate when the control is carried out in a disorderly manner.Thereupon, in order to monitor both of the controls, a control system 8selects from (A) or (B) and controls which is the first part of the flowchart shown in FIG. 11. In this embodiment, (B) is given priorityimmediately after the beginning of the laser oscillation, and (A) isgiven priority after the operation is stabilized to a certain extent.

Next, explanation is given on time sharing control with reference toFIG. 12. The device in this case is, for example, as shown in FIG. 14.

First of all, in Step 42, the laser output is measured by the powermonitor system 9, and in Step 43, the measured data isaverage-mean-processed N times by a time sharing control means 53 tocalculate the present laser output value P_(N). Next, the Step 44, theabsolute value |ΔP| of the difference between P_(N) and the designatedlaser output value P_(O) (the value which can be set from the exterior)is calculated, and in Step 45, the value of |ΔP| is compared with thevariation permissive value P_(A) (the value which can be set from theexterior). When |ΔP|>P_(A), in Step 46, it is judged that whether theapplied voltage is controlled with time sharing from the value of thepresent applied value or the etalon for rough tuning is controlled. Forexample, in the case where the applied voltage is the preset lower limitvoltage and lower, the output is controlled only by the applied voltage,and in the case where the applied voltage is the lower limit voltage andlarger or is the preset upper limit voltage and higher, the controls ofthe applied voltage and the etalon for rough tuning are switched in avariable time interval and are controlled alternately. Further, in thecase where the applied voltage exceeds the upper limit voltage, thecontrol is carried out so that the output of only the etalon for roughtuning is a maximum. In such a way, control is switched depending uponthe magnitude of the applied voltage.

And in the case where the applied voltage is controlled, in Step 47, thecontrol quantity of the applied voltage is calculated from |ΔP|, and innext Step 48, it is determined whether the applied voltage is toincrease or to decrease. According to this result, in Step 49, theapplied voltage is controlled so that the laser output is constant. Inthe case where the etalon for rough tuning 4 is controlled, in Step 50,the control quantity of the etalon for rough tuning 4 is calculated, andin next Step 51, which direction the etalon for rough tuning 4 is to becontrolled is determined from the polarity of ΔP×P_(N) -P_(O), and inStep 52, the etalon for rough tuning 4 is adjusted so that the laseroutput is constant using the servo system 11. In addition, in the casewhere |ΔP|≦P_(A), the oscillation is continued intact. By continuing theoperation during the oscillation, the laser output is controlled to beconstant.

In some embodiments among the above described, an etalon is used aswavelength monitor system, however, it is to be understood thatspectroscopy elements such as Fizeau's interferometer, grating, prism,and the like may be used. They have the same effects as aforesaidembodiments by measuring spectro-light intensity distribution.

And in the above embodiments, the method of driving an etalon for finetuning is performed by calculating the wavelength deviation according toimage processing of the light intensity distribution of the laser light,but it is without saying that any method capable of doing wavelengthmonitor can be substituted therefor and the same effect can be obtainedwithout image processing. As a method of not image processing the lightintensity distribution, there is a method, for example, wherein theetalon for fine tuning can be controlled by allocating an optical sensorto x=x_(O) shown in FIG. 3 and using it as the wavelength monitorsystem, and by changing the etalon for fine tuning from the optimalstate to back and forth, and by anticipating the direction of the mostoptimal state of the etalon for fine tuning from the changing optimalstate of the etalon for the fine tuning from the changing extent oflight intensity in X=X_(O) at that time.

INDUSTRIAL AVAILABILITY

This invention can be applied to the wavelength stabilizing of laserapparatus, for example, an excimer laser device.

What is claimed is:
 1. A laser device having a stabilized wavelengthcomprising:a light resonator having a laser medium therein forgenerating a laser beam; a first etalon within said resonator for finetuning spectral characteristics of said laser beam; a second etalonwithin said resonator for coarse tuning spectral characteristics of saidlaser beam; means for monitoring the wavelength of the laser beam afterthe beam exits the resonator; means for measuring an output power ofsaid laser beam; means for controlling the first etalon based on saidmeasured wavelength; and means for controlling the second etalon basedon said measured power.
 2. A method of stabilizing the wavelength of alaser beam comprising the steps of:measuring the wavelength of a laserbeam; measuring an output power of said laser beam; controlling a firstetalon in accordance with the measured wavelength to stabilize thewavelength of the laser beam; and controlling a second etalon inaccordance with the measured output power to stabilize the power of thelaser beam.
 3. A method of stabilizing the wavelength of a laser beamcomprising the steps of:measuring the wavelength of said laser beam;controlling a first etalon in accordance with said measured wavelengthto stabilize said wavelength; detecting an output power of said laserbeam; calculating a difference between the output power and apredetermined objective power; and controlling a second etalon so thatthe difference in minimized when the difference exceeds a permissiblevalue.
 4. A method for stabilizing the wavelength of a laser beamgenerated in a laser medium comprising the steps of:measuring thewavelength of the laser beam; measuring a voltage applied to the lasermedium; controlling a first etalon based on the measured wavelength tostabilize the wavelength of the laser beam; and controlling a secondetalon based on the measured applied voltage to stabilize an outputpower of said beam.
 5. A laser device for generating a laser beam havinga stabilized wavelength comprising:a light resonator having a lasermedium therein for generating a laser beam; a first etalon within saidresonator for fine tuning spectral characteristics of said laser beam; asecond etalon within said resonator for coarse tuning spectralcharacteristics of said laser beam; means for measuring the wavelengthof the laser beam; means for measuring a voltage applied to said lasermedium; means for controlling the first etalon based on said measuredwavelength; and means for controlling the second etalon based on saidmeasured applied voltage.
 6. A method for stabilizing the wavelength ofa laser beam generated in a laser medium comprising the stepsof:measuring the wavelength of the laser beam; controlling a firstetalon based on said measured wavelength in order to stabilize saidwavelength; measuring an output power of said laser beam; controlling avoltage applied to said laser medium in accordance with said measuredoutput power; measuring said applied voltage; and controlling a secondetalon based on said measured applied voltage.
 7. A method forstabilizing an output wavelength of a laser beam generated in a lasermedium comprising the steps of:measuring the wavelength of said laserbeam; controlling a first etalon based on said measured wavelength tostabilize said output wavelength; detecting a voltage applied to saidlaser medium; calculating a difference between said applied voltage anda predetermined object voltage; and controlling a second etalon suchthat said difference in minimized.
 8. A method of stabilizing an outputwavelength of a laser beam generated in a laser medium comprising thesteps of:measuring the wavelength of said laser beam; controlling afirst etalon based on said measured wavelength to stabilize said outputwavelength; measuring an output power of said laser beam; determiningwhether to adjust either a voltage applied to said laser medium or asecond etalon in order to stabilize said output power; and adjustingeither said applied voltage or said second etalon based on saiddetermination.
 9. A laser beam generating device comprising:a lightresonator having a laser medium therein for generating a laser beam;first etalon for fine tuning spectral characteristics of said laserbeam; a second etalon for coarse tuning spectral characteristics of saidlaser beam; means for measuring an output wavelength of said laser beam;means for controlling said first etalon based on said measuredwavelength; means for measuring an output power of said laser beam; andmeans for controlling one of said second etalon or a voltage applied tosaid laser beam, whereby the output power of said laser beam isstabilized.